Michigan’s Existing Digital Message Signs Evaluated Through Several Field Case Studies on Safety and Mobility.
Digital Message Signs (DMS) (also referred to as dynamic message signs, variable message signs, or changeable message signs) are an important part of the Advanced Traveler Information Systems (ATIS) that display a variety of real-time travel information for the road users, including traffic diversion, travel time, congestion, upcoming roadwork, lane closures, and incidents such as traffic accidents. Other information includes inclement weather, speed regulations, special events, and safety related messages such as seatbelt usage. Given limited budgets and time constraints, it is important for DOTs to be aware of the most efficient DMS practices. Therefore, this study evaluated different DMS message types and installation locations in Grand Rapids, Saugatuck, and Saginaw, Michigan by developing a data-driven methodology involving field case studies and user surveys, utilizing a variety of data collected from 2019 to 2021. The study also generated results to facilitate better allocation of Michigan DOT’s (MDOT) resources by investing in effective sign technologies for traffic improvement and improve overall DMS operational practices.
Several field case studies were conducted to understand the effectiveness of particular messages and types of DMS, including weather-related DMS messages on driver speeds; exploring the feasibility of automating message display through Environmental Sensor Station (ESS) data; an assessment of the effectiveness of certain weather-related messages; verifying the accuracy of travel times displayed on DMS, identifying factors that influence travel time fluctuations, and quantifying the influence of DMS messages on traffic rerouting. A separate case study was executed to assess the benefits of deploying Portable Changeable Message Signs (PCMS) at a construction location. Lastly, cost-benefit analyses for selected cases were carried out. In addition to the field case studies, online driver surveys were conducted in phases from June 2020 to February 2021 with a total of 929 responses, to understand public perception of DMS effectiveness. Other data collected included Microwave Vehicle Detector Sensor (MVDS), Continuous Counting Station (CCS) data for 2019, archived probe vehicle travel time, DMS operational messages for 2019, weather records from ESS, field travel time (using Bluetooth sensors), and lab-based virtual reality (VR) simulation data based on 26 participants.
- The evaluation of the effect of weather-related messages on traffic speeds showed that the notice “ROAD MAY BE SLIPPERY, REDUCE SPEED” led to a speed reduction of 5.66 mph by drivers driving above 80 mph, immediately after they saw the message on the DMS.
- Evaluation of the impact of displaying alternative routes’ travel times on drivers’ decision making (traffic diversion) revealed that the chances of drivers opting for an alternative route rose by 35 percent if it saved a minute compared to their initially preferred route.
- Using PCMS to notify of upcoming lane closures led to a 3.18 percent increase in vehicles merging early and reduced travel time across the work zone by 5.54 percent.
- The VR study, despite its limited participant number, suggested that the readability of DMS messages with a 4-second phasing time were lower than those with a 2.5-second phase time.
- Driver surveys revealed that 71 percent “extremely agreed” with the statement that they could read the entire message when displayed on a single screen, and 62 percent said that DMSs are “extremely useful in guiding their response to a full road closure due to roadwork”.
- The benefit-cost ratio (BCR) calculated by dividing the daily savings from PCMS by the installation and operation cost, was 0.41. The researchers recommended use of PCMS in high traffic work zones on freeways to get higher BCR values reaching the breakeven point (BCR=1) faster.
- The benefit-cost analysis indicated that the break-even point for a DMS, accounting for a 5.66 mph speed reduction, would be within the second year of a 15-year service life.
- The BCR value for the traffic diversion field case study was calculated as 1.012 considering travel time savings benefits and DMS installation and maintenance costs.